Optical properties of doped and undoped Vanadium dioxide thin films on Sapphire substrate at near-infrared and terahertz frequencies
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Terahertz (THz) waves have many applications in areas such as security screening, material characterization, biomedical imaging and communications. However, at this frequency range there is a lack of optical components such as optical switches, filters and modulators. Among many materials used in THz device applications, vanadium dioxide (VO2) is of particular importance. VO2 experiences a fast reversible insulator-to-metal phase transition (MIT) at ~68 °C temperature. This material property is accompanied by significant changes in VO2 electrical and optical properties especially in the THz and infrared (IR) regions of the electromagnetic spectrum. In this dissertation, I studied the optical properties of doped and undoped VO2 thin films in the THz and IR range for a variety of applications. Terahertz Time-Domain Spectroscopy (THz-TDS) was used in order to investigate the THz transmission properties of VO2. The first chapter focuses on effects of tungsten-doping on the electrical and optical properties of VO2 thin films in the THz range and its application to future analog based devices by taking advantage of the gradual phase transition window. Similarly, in the second chapter I explored the effects of hydrogen-doping and its THz antireflection applications at room temperature. The third chapter presents a Gires-Tournois Etalon structure that can operate in the THz range. Etalons can be prospectively used in THz pulse amplification, THz lasers and THz sensing. The properties of the etalon can be dynamically controlled by making use of phase transition of VO2. In the last chapter I investigated the optical properties of VO2 thin films deposited on each side of a sapphire substrate. This approach allows for larger amplitude modulation which is an important requirement in optical switching applications.